The goal of surgical manipulator systems is to apply robotic and sensor technologies to improve the quality of patient surgical outcomes in a cost-effective manner. Surgical robotics can attain this goal through repeatable increased spatial resolution and better geometric accuracy of surgical tools positioning by the surgeon, faster operating speed, good ergonomics that can reduce the surgeon's fatigue, and the ability to provide a platform for surgeon training and education.
A number of commercial surgical robotic systems are currently in use including the NeuroArm Magnetic Resonance Imager (MRI) compatible neurosurgical robot by the University of Calgary, the da Vinci and Zeus surgical robots by Intuitive Surgical, the RAMS system by Microdexterity and the Jet Propulsion Laboratory, the Haptic Guidance System by MAKO, the SpineAssist by Mazor Surgical Technologies, as well as ROBODOC of Integrated Surgical Systems. For a list of reference to the existing patents of the above-mentioned systems, refer to the appendix.
The University of Calgary neuroArm system is designed to perform neurosurgery in an MRI environment. It has dual arms, each with 6 Degrees of Freedom in a master-slave configuration. The robot is MR compatible so no magnetic material is used for any part of the robot arm. It also has haptic feedback capability for sensing tool tip forces. Surgical tool changes are performed manually, see U.S. Pat. No. 7,155,316. The Intuitive Surgical da Vinci system is designed for laparoscopic surgery. It can have up to 5 arms controlled by the surgeon in a Master-slave control configuration. The system is large and heavy with a weight greater than 1000 lbs. There is no haptic feedback and tool changes are performed manually. The Zeus is a discontinued product that was also designed for laparoscopic surgery. Smaller and lighter than the da Vinci, the Zeus also had up to 5 arms in a Master-slave control architecture with no haptic capability and manual tool changes. (di Vinci: patents see attached list; Zeus: U.S. Pat. Nos. 5,515,478, 5,553,198, 5,645,520, 6,646,541, 6,714,841 etc)
Originally developed by JPL, the Robot-Assisted Micro-Surgery (RAMS) system is being commercialised by MicroDexterity. This telerobotic platform is designed for microsurgery on brain, eye, ear, nose, throat, face, and hand. Clinical tests had been performed on neurosurgery and hand surgery. The dual-arm system is very compact; the manipulator is approximately 25 mm in diameter and 250 mm long. The robot has a Master-slave architecture and exhibits high spatial resolution of 10 microns. The system has indirect pressure and texture sensing of the tool forces using joint encoder information. The surgical tools are changed manually, see U.S. Pat. No. 6,702,805.
The MAKO Haptic Guidance System targets knee replacement surgeries by means of a robotic system that assists the surgeon in arthroplasty through keyhole incisions. The FDA-approved system allows surgeon to pre-operatively optimize the size and alignment of knee, and execute surgeon-guided knee sculpturing and implant placing with CT image-guidance, see US patent Publications 20060142657, 07206627, 07139418)
Mazor Surgical Technologies developed the SpineAssist as a minimally invasive guidance systems for pedicle screw insertion as well as other spine related procedures. In the size of a soda can, the SpineAssist is a parallel-platform robot mounted onto the patient's spine or spinous process. Pre-operative planning with CT images is followed by automatic fluoroscope or CT image registration to the robot, after which the positioning device automatically directs its arm in the trajectory planned by the surgeon, with accuracy less than 1.5 mm.
In 1992, Integrated Surgical Systems introduced the ROBODOC, a large orthopedic surgical system intended for use in patients requiring primary cementless total hip replacement surgery. It has a single 6DOF arm that operates automatically using a pre-operatively defined program. It has no haptic feedback capability and tool changes are performed manually, see US Patent Publications 20040142803, 05766126, 06239874, 06349245.
The Pathfinder developed by Prosurgics is a stereotaxy tool-locator with image-guidance capabilities for intracranial neurosurgeries. The arm has six degrees-of-freedom and is passively manipulated by the surgeon without haptic feedback. The single-arm system is mounted on a mobile base. Surgical tools are changed out manually.
Laprotek is a minimally-invasive surgical robotics system. Developed by endoVia, the system is similar to Zeus. It has two four degrees-of-freedom arm teleoperated by joysticks at a console, with visual feedback also available via laparoscopic camera. It has haptic feedback using force sensors at the motors.
There are a number of aspects of the existing state of surgical robotic technology that require major improvements. The development of robot arms that are dexterous, precise and have large workspaces both in how they attain the work site location and when they are inside body cavities and organs. The overall size, weight and volume of most current systems are a major issue in that they have a major detrimental impact on operating room facility space and the support staff who set-up the equipment. Smaller, lighter weight stowable systems are needed. For example, the da Vinci surgical manipulator weighs 1200 lbs (exclusive of the operator interface) and stands approximately 8 ft. The Zeus arms are approximately 2 ft long and weigh 40 lbs. Total weight of the robot is 120 lbs. (exclusive of the user interface).
The majority of current systems do not provide Haptic feedback. Haptic feedback restores the lost sense of touch for the surgeon and may improve the surgeon's performance in terms of speed and reducing risk of collateral tissue damage.
Manual surgical tool exchange increases the surgical operating time; increasing the time the patient is required to remain under anaesthesia and increasing facility costs. The ability to automatically exchange surgical tools would therefore reduce patient risks and lower operating costs.
The high mechanical power density and small diameter of conventional dc motor servomotors are desirable traits to reduce the physical dimensions of robotic manipulators. However, the drawback of conventional servomotors presently in use in many surgical robots is their long axial length, so a right-angle transmission means is needed if excessive lateral extension of the manipulator arm joints is to be avoided.
Of all the available right-angle transmission components at present, bevel gear pairs deliver high torque and backdrivability, but backlash is typically high and they seldom come in small packages. The traditional standard bevel gear box has large backlash in transmission which is highly undesirable in applications where high precision is required in both directions of motion.
There are several manufacturers offering worm gears in a small package, and integrating with spring-loaded features the gearbox can be backlash free and achieve precise motion, but the lowered efficiency and the odd standard gear ratio increment suggest that more powerful (thus larger in size) motors will be needed. Worm gear boxes can have low-backlash configurations but its indirect proportional relationship between the efficiency versus the gear ratio leads to a bulkier and heavier overall unit, while also the lack of back-drivability is also undesirable in the event of crash recovery or calibration common to robotics applications.
Cable-pulley system provides an alternative to traditional gear-type mechanism, but introduces transmission error if any of the cable segments in the transmission chain is not tensioned properly. Researchers from Massachusetts Institute of Technology and eventually Barrett Technology developed the WAM, or the “whole-arm-manipulation”, in which part of the mechanism involves a differential cable-pulley subset that allows for a two degree-of-freedom motion at the same joint driven by two independent motors. Cable within the WAM design is pretensioned at a single-point by turning two coaxial pulleys independently with cable responsible for both directions forming a U-shape turnaround at termination for auto-adjustment of cable length and tensioning automatically. Another differential pulley application can be found at the hoist and drive concept by Power Kinetics, in which cable pretension is accomplished by increasing the physical separation between pulleys. Commissariat a l'Energie Atomique, meanwhile, created a two to three degrees-of-freedom mechanism, using idle pulleys for both redirecting the direction of cable and also tensioning the cable. On the other hand, Roto-Lok mechanism developed by Sagebrush Technology is a parallel drum-drive configuration using cable and pulleys. Springs are presented at each of the cable termination to eliminate transmission slack. For a list of patents on the above-mentioned mechanisms refer to the appendix section. None of the above mentioned inventions can be adapted to a single-actuator right-angle transmission application, and their means of cable tension adjustment all require extra room for additional elements which will lead to the increase in overall size of the transmission module.
Harmonic drives, on the other hand, features zero-backlash, highly repeatable precision, back-drivability, high efficiency, compact size and lightweight. Unfortunately, the mechanism does not allow for a right-angle drive version. No commercially available right-angle transmission in the market currently has both zero-backlash and high efficiency capabilities in a compact in-line package.
Therefore, it would be very advantageous to provide a surgical robotic system employing right angle drives which avoids the above mentioned drawbacks.